F150 COIL ON PLUGS

I HAVE A 05 FORD F-150 WITH THE 4.5 LITER ENGINE.I" VE HAD TO REPLACE TWO OF THE COILS(AT THE DEALERS) AND NOW ITS ACTING LIKE IT WAS BEFORE I REPLACED THEM SO THERE'S ANOTHER ONE BAD. QUESTION. IS THERE ANY WAY I CAN TEST THE COILS MYSELF TO FIND THE BAD ONE? THANKS FOR ANY HELP AND BEST REGARDS.P.S. I'LL TAKE AN OLD CAR ANYDAY.